The invention relates more particularly to a method for ejecting a vessel, in particular a preform made of thermoplastic material, carried by a transport device, in which the vessel is provided with a cylindrical neck with a vertical axis that comprises a free upper end edge called a mouth, with the transport device comprising:                At least one movable support along a path;        At least one mandrel for gripping the vessel by vertical engagement with the neck, with the gripping mandrel being mounted to rotate on the movable support to make possible the rotation of the vessel around the axis of the neck during its transport;        A lower ejection face that is mounted on the movable support, with the gripping mandrel being mounted to slide vertically relative to the ejection face for making it possible to extract the gripping mandrel from the neck during relative sliding of it by bringing the ejection face into contact with an upper bearing face vertically opposite the neck, with the gripping mandrel sliding relative to the ejection face between a lower transport position in which the engagement of the gripping mandrel with the neck is made possible and an upper ejection position of the vessel in which the ejection face prevents the gripping mandrel from engaging with the neck by abutment against the bearing face of the neck.        
It is known to manufacture vessels made of thermoplastic material by forming preforms, for example by blow molding or by stretch blow molding.
The preforms are in general manufactured by injection. A preform has a body that is intended to be stretched to be shaped into the final vessel during the forming operation. The neck of the preform already has its final shape. It is therefore important to protect the neck throughout the process for transformation of the preform into the final vessel.
To carry out the forming operation, it is necessary to heat in advance the bodies of the preforms at a glass transition temperature so as to make them malleable. The facilities for mass-producing vessels for this purpose comprise furnaces for heating preforms.
A heating furnace in general has the shape of a tunnel in which at least one of the walls comprises heating means. The preforms move along the tunnel in front of the heating means while turning round and round so that their bodies are heated in a uniform manner to a temperature that is suitable for the forming operation.
For this purpose, the furnace comprises a device for transporting preforms that in general come in the form of a closed chain, each link of which forms a movable support that is provided with means for gripping a preform.
Each preform is gripped by a mandrel that is engaged with the neck of the preform. The mandrel is, for example, formed by a mandrel with radial expansion that is forced into the neck of the preform.
At the outlet of the furnace, the preforms are transferred to a blow-molding station by means of a transfer wheel. During the passage of preforms from the furnace to the transfer wheel, the mandrels are extracted from the neck of the preforms so that the preforms are ejected from the transport device. The thus ejected preforms are received in suitable slots of the transfer wheel.
The machines for mass-producing vessels should allow preforms to move at high speed in the furnace. This involves being able to eject the preforms from their gripping mandrel at a fast enough rhythm not to slow down the movement of the preforms into the furnace.
In the known ejection methods, the movable support is provided with an ejection face that comes into contact with a portion of the mouth of the neck of the vessel when the ejection mandrel slides toward its upper position. The preform is then held in a lower position by the ejection face, while the mandrel continues its sliding toward its upper position until the extraction of the mandrel in the manner of a corkscrew is complete. This method is satisfactory because it makes possible a fast ejection of the preforms.
Nevertheless, the mouth is sometimes damaged by its contact with the ejection face.
In addition, the mouth is a portion of the neck that is likely to come into contact with the liquid that is contained in the final vessel. For certain contents of the vessel, in particular for food as contents, the vessel is to meet standards as regards its sterilization. However, the contact of the mouth with the ejection face may involve a risk of contamination of the liquid that is contained in the vessel. It is therefore sometimes required to sterilize the ejection face.
In addition, the mouth of the vessel is intended to come into contact with a face for positioning the mandrel to make possible an optimal positioning of the preform relative to the mandrel. This ensures that the preform thus occupies a vertical position that is determined relative to the mandrel, and this also ensures that the axis of the neck of the preform is perfectly coaxial with the axis of rotation of the mandrel.
The positioning face in general has an annular shape so as to come into contact with an inside annular portion of the mouth. This makes it possible to release an outside annular portion of the mouth for contact with the ejection face.
Nevertheless, it has been observed that the sharing of the mouth between its positioning function and its ejection function could result in poor ejection of the preform or poor positioning of the preform, in particular when the preform has a neck whose wall is very fine.